Bonded abrasive article including elongate shaped abrasive particles

ABSTRACT

A bonded abrasive article includes elongate shaped abrasive particles. The elongate shaped abrasive particles comprise an elongate shaped ceramic body having opposed first and second ends joined to each other by at least two longitudinal sidewalls. At least one of the at least two longitudinal sidewalls is concave along its length. At least one of the first and second ends is a fractured surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. application Ser.No. 16/087,013, filed Sep. 20, 2018, which is a national stage filingunder 35 U.S.C. 371 of PCT/2017/023726, filed Mar. 23, 2017, whichclaims the benefit of U.S. Provisional Application No. 62/316,854, filedApr. 1, 2016.

TECHNICAL FIELD

The present disclosure broadly relates to elongate abrasive particles,methods of their manufacture, and their use in abrasive articles.

BACKGROUND

Elongate abrasive filaments are used in bonded abrasive articles.Precursor filaments (typically of a sol-gel ceramic precursor) areextruded and cut or broken to desired lengths, and then fired. Theresultant abrasive filaments (sometimes termed “rods”) are used inabrasive products such as bonded abrasive wheels, for example. However,in such processes it is difficult or impossible to precisely control theshape of the abrasive filaments; for example, due to curling of thefilaments during the extrusion process. There is a need for new methodsof making elongate abrasive particles. Further, there is a continuingneed for new abrasive particle shapes that can provide improved abradingperformance, especially in bonded abrasive articles.

SUMMARY

Above-identified needs in the art are provided according to the presentdisclosure. Advantageously, abrasive particles having elongate ceramicbodies according to the present disclosure have a concave side thatextends longitudinally along the surface of the particles, which createssharp ridges which may enhance abrasive performance. Further, the methodcan be practiced using inexpensive off-the-shelf molds.

In one aspect, the present disclosure provides an elongate shapedabrasive particle comprising an elongate shaped ceramic body havingopposed first and second ends joined to each other by at least twolongitudinal sidewalls, wherein at least one of the at least twolongitudinal sidewalls is concave along its length, and wherein at leastone of the first and second ends is a fractured surface.

In another aspect, the present disclosure provides a plurality ofelongate shaped abrasive particles, wherein at least half of theplurality of elongate shaped abrasive particles comprises elongateshaped abrasive particles according to the present disclosure. Thepresent disclosure also provides a bonded abrasive article comprisingthe plurality of elongate shaped abrasive particles bonded together by abinder material.

In yet another aspect, the present disclosure provides a method ofmaking a plurality of elongate shaped abrasive particles, the methodcomprising sequential steps:

-   -   a) providing a mold having a plurality of isolated open-ended        grooves disposed on a major surface thereof;    -   b) filling at least a portion of the plurality of isolated        open-ended grooves with a molding composition comprising a        ceramic precursor material and a volatile liquid;    -   c) removing any excess molding composition not disposed within        the plurality of isolated open-ended grooves, if present, from        the mold;    -   d) removing a sufficient amount of the liquid vehicle to provide        a plurality of dimensionally stable elongate precursor bodies;        and    -   e) converting at least a portion of the plurality of        dimensionally stable elongate precursor bodies into the elongate        shaped abrasive particles, each comprising, respectively, an        elongate shaped ceramic body having opposed first and second        ends joined to each other by at least two longitudinal        sidewalls, wherein at least one of the at least two longitudinal        sidewalls is concave along its length, and wherein at least one        of the first and second ends is a fractured surface.

As used herein:

-   -   the term “aspect ratio” refers to the ratio of average length to        average thickness;    -   the adjectives “elongate” and “elongated” mean having an aspect        ratio of at least 2;    -   the term “fractured surface” refers to a surface formed by a        fracturing process;    -   the term “isolated” used in reference to parallel open-ended        grooves, means that the parallel open-ended grooves are not        interconnected by intersecting grooves (e.g., a lattice        pattern);    -   the term “length” refers to the longest dimension of an object;    -   the term “width” refers to the longest dimension of an object        that is perpendicular to its length;    -   the term “thickness” refers to the longest dimension of an        object that is perpendicular to both of its length and width;        and    -   the term “shaped ceramic body” refers to a ceramic body having a        shape at least partially determined by a mold (e.g., an open        face mold) used in its manufacture (e.g., it is determined by        the shape of a corresponding mold cavity used in its        manufacture).

Features and advantages of the present disclosure will be furtherunderstood upon consideration of the detailed description as well as theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D are schematic perspective views of respective molds 100a-100 d.

FIG. 2 is a schematic perspective view of an elongate shaped abrasiveparticle 200 according to the present disclosure.

FIG. 3 is a schematic perspective view of an elongate shaped abrasiveparticle 300 according to the present disclosure.

FIG. 4 is a schematic perspective view of a bonded abrasive wheelaccording to the present disclosure.

FIG. 5 is an optical micrograph of elongate shaped abrasive particlesproduced in Example 1.

FIGS. 6A and 6B are SEM micrographs of the tool used to prepare theelongate shaped abrasive particles of Example 2.

FIGS. 7A and 7B are SEM micrographs of elongate shaped abrasiveparticles prepared in Example 2.

Repeated use of reference characters in the specification and drawingsis intended to represent the same or analogous features or elements ofthe disclosure. It should be understood that numerous othermodifications and embodiments can be devised by those skilled in theart, which fall within the scope and spirit of the principles of thedisclosure. The figures may not be drawn to scale.

DETAILED DESCRIPTION

Methods according to the present disclosure method for making elongateabrasive particles may include a number of steps carried outsequentially. It is not necessary that any of the steps be carried outconsecutively, although in some embodiments it may be preferred to carryout at least some (or even all) of the sequential steps consecutively.

In the first step a mold is provided. The mold has a plurality ofisolated open-ended grooves disposed on a major surface thereof. Thegrooves may be linear, curved, or a mixture of linear and groovedportions. Individual grooves may be different in shape (when viewednormal to the mold surface), width, length, cross-sectional profile,and/or depth. In some preferred embodiments, all of the grooves areidentical. In some preferred embodiments, the grooves are linear andparallel. In some preferred embodiments, the grooves are identical,linear, and parallel. In general, the grooves are open at the surface ofthe mold, and the ends of grooves extend across the mold surface to thesides, where they are open at their ends. Preferably, the isolatedgrooves have constant cross-sectional shape and area along theirlengths, although this is not a requirement.

In order to form elongate ceramic bodies, the grooves themselves shouldhave an aspect ratio of at least 2, preferably, at least 5, at least 10,at least 15, at least 20, at least 30, at least 40, at least 50, or evenmore.

FIGS. 1A-1D illustrate various possible mold 100 a-100 d configurationsof grooves 110 a-110 d. For example, in FIG. 1A, mold 100 a has linearparallel isolated grooves 110 a with rounded bottoms 120 a with asemicircular transverse cross-sectional shape. In FIG. 1B, mold 100 bhas linear parallel isolated grooves 110 b with two parallel verticalsidewalls 122 b contacting a flat bottom 120 b. In FIG. 1C, mold 100 chas linear parallel isolated grooves 110 c with two parallel verticalsidewalls 122 c contacting a rounded bottom 120 c. In FIG. 1D, mold 100d has isolated grooves 110 d with a v-shaped bottom 120 d.

In a second step, at least a portion of the plurality of isolatedopen-ended grooves are filled with a molding composition comprising aceramic precursor material and a volatile liquid.

Exemplary ceramic precursor materials include: transitional aluminas(e.g., boehmite, diaspore, gibbsite, bayerite, nordstrandite); aluminumsalts and complexes such as, for example, basic aluminum carboxylates(e.g., basic aluminum carboxylates of the general formulaAl(OH)y(carboxylate)3-y, where y is between 1 and 2, preferably between1 and 1.5, and the carboxylate counterion is selected from the groupconsisting of formate, acetate, propionate, and oxalate, or combinationsof these carboxylates, aluminum formoacetate, and aluminumnitroformoacetate); basic aluminum nitrates; partially hydrolyzedaluminum alkoxides; and combinations thereof. Basic aluminumcarboxylates can be prepared by digesting aluminum metal in a solutionof the carboxylic acid as described in U.S. Pat. No. 3,957,598 (Merkl).Basic aluminum nitrates can also be prepared by digesting aluminum metalin a nitric acid solution as described in U.S. Pat. No. 3,340,205 (Hayeset al.) or British Pat. No. 1,193,258 (Fletcher et al.), or by thethermal decomposition of aluminum nitrate as described in U.S. Pat. No.2,127,504 (Derr et al.). These materials can also be prepared bypartially neutralizing an aluminum salt with a base. The basic aluminumnitrates have the general formula Al(OH)_(z)(NO₃)_(3-z), where z is fromabout 0.5 to 2.5.

Suitable boehmites include, for example, those commercially availableunder the trade designation “HIQ” (e.g., HIQ-9015) from BASF Corp.,Florham Park, N.J., and those commercially available under the tradedesignations “DISPERAL”, “DISPAL”, and “CATAPAL D” from Sasol NorthAmerica, Houston, Tex. In some embodiments, the ceramic precursor maycomprise, alone or in addition, fine alpha alumina particles that uponsintering fuse together to form a sintered alpha alumina ceramic body,e.g., as disclosed in U.S. Publ. Pat. Appln. No. 2016/0068729 A1(Erickson et al.).

The ceramic precursor material should comprise a sufficient amount ofthe liquid vehicle for the viscosity of the composition to besufficiently low to enable filling the mold cavities, but not so muchliquid as to cause subsequent removal of the liquid from the moldcavities to be prohibitively expensive. In some preferred embodiments,the ceramic precursor material comprises an alpha alumina precursor.

Further details regarding alpha alumina precursor, including methods formaking them and converting them into abrasive particles, can be found,for example, in U.S. Pat. No. 4,314,827 (Leitheiser et al.); U.S. Pat.No. 4,623,364 (Cottringer et al.); U.S. Pat. No. 4,744,802 (Schwabel);U.S. Pat. No. 4,770,671 (Monroe et al.); U.S. Pat. No. 4,881,951 (Woodet al.); U.S. Pat. No. 5,011,508 (Wald et al.); U.S. Pat. No. 5,090,968(Pellow); U.S. Pat. No. 5,201,916 (Berg et al.); U.S. Pat. No. 5,227,104(Bauer); U.S. Pat. No. 5,366,523 (Rowenhorst et al.); U.S. Pat. No.5,547,479 (Conwell et al.); U.S. Pat. No. 5,498,269 (Larmie); U.S. Pat.No. 5,551,963 (Larmie); U.S. Pat. No. 5,725,162 (Garg et al.); U.S. Pat.No. 5,776,214 (Wood); U.S. Pat. No. 8,142,531 (Adefris et al.); and U.S.Pat. No. 8,142,891 (Culler et al.).

In one exemplary embodiment, the ceramic precursor material comprises asol-gel composition comprises from 2 to 90 weight percent of an alphaalumina precursor material (e.g., aluminum oxide monohydrate(boehmite)), and at least 10 weight percent, from 50 to 70 weightpercent, or 50 to 60 weight percent, of volatile components such aswater. In some embodiments, the sol-gel composition contains from 30 to50 weight percent, or 40 to 50 weight percent of the alpha aluminaprecursor material. As used herein, the term “sol-gel composition”refers to a colloidal dispersion of solid particles in a liquid thatforms a three-dimensional network of the solid particles on heating overa period of time, or removal of some of the liquid. In some cases, gelformation may be induced by addition of polyvalent metal ions.

A peptizing agent can be added to the sol-gel composition to produce amore stable hydrosol or colloidal sol-gel composition. Suitablepeptizing agents are monoprotic acids or acid compounds such as aceticacid, hydrochloric acid, formic acid, and nitric acid. Multiprotic acidscan also be used but they can rapidly gel the sol-gel composition,making it difficult to handle or to introduce additional componentsthereto. Some commercial sources of boehmite contain an acid titer (suchas absorbed formic or nitric acid) that will assist in forming a stablesol-gel composition.

Seed particles and/or crystal grain size modifiers may optionally beadded to the sol-gel composition, but advantageously they are typicallynot needed in order to achieve small alpha alumina crystal grain sizes.

Examples of optional alumina grain size modifiers include Li₂O, Na₂O,MgO, SiO₂, CaO, SrO, TiO₂, MnO, Cr₂O₃, Fe₂O₃, CoO, NiO, ZnO, ZrO₂, SnO₂,HfO₂, rare earth oxides (e.g., La₂O₃, CeO₂, Pr₂O₃, Nd₂O₃, Sm₂O₃, Eu₂O₃,Gd₂O₃, Dy₂O₃, Er₂O₃, Yb₂O₃, TbO₂, Y₂O₃), combinations thereof, andprecursors thereof. In some embodiments, the ceramic precursor material,and hence the corresponding ceramic abrasive particles, are essentiallyfree of any or all of the foregoing and/or other alumina grain sizemodifiers.

The alpha alumina precursor may be “seeded” with a material having thesame crystal structure as, and lattice parameters as close as possibleto, those of alpha alumina. The “seed” particles are added in as finelydivided form as possible, and are dispersed uniformly throughout the solor gel. Seed particles can be added ab initio or it can be formed insitu. The function of seed particles is to cause the transformation tothe alpha form to occur uniformly throughout the alpha alumina precursorat a much lower temperature than is needed in the absence of the seed.Suitable seeds include alpha alumina itself and also other compoundssuch as alpha ferric oxide, chromium suboxide, nickel titanate and aplurality of other compounds that have lattice parameters sufficientlysimilar to those of alpha alumina to be effective to cause thegeneration of alpha alumina from a precursor at a temperature below thatat which the conversion normally occurs in the absence of such seed.Examples of suitable seed particles include particles of Ti₂O₃,MgO.TiO₂, FeO.TiO₂, NiO.TiO₂, CoO.TiO₂, MnO.TiO₂, ZnO.TiO₂, V₂O₃, Ga₂O₃,Rh₂O₃, alpha-Al₂O₃, alpha-Cr₂O₃, and alpha-Fe₂O₃ particles, preferablyhaving an average particle size of from about 10 nm to about 120nanometers, although other sizes may be used. In some embodiments, theprecursor particles, and likewise the derived ceramic abrasiveparticles, are essentially free of seed particles such as, for example,alpha-Al₂O₃ seed particles, alpha-Cr₂O₃ seed particles, or alpha-Fe₂O₃seed particles.

Sol-gel compositions can be formed by any suitable means, such as, forexample, simply by mixing aluminum oxide monohydrate with watercontaining a peptizing agent or by forming an aluminum oxide monohydrateslurry to which the peptizing agent is added. Defoamers and/or othersuitable chemicals can be added to reduce the tendency to form bubblesor entrain air while mixing. Additional chemicals such as wettingagents, alcohols, and/or coupling agents can be added if desired.

The molding composition may have any suitable form and/or composition,but preferably comprises a sol-gel composition (i.e., a dispersion ofcolloidal ceramic precursor particles), a slurry, or a viscous solution.

Exemplary volatile liquids include, water, alcohols, ethers, ketones,and ester alcohols. Preferably, the volatile liquid comprises at least 5percent, at least 20 percent, at least 40 percent, at least 60 percent,at least 80 percent, or even 100 percent by weight of water.

The molding composition may be introduced into the grooves by anydesired means. Flood coating, roll coating, or curtain coating may beused to introduce the molding composition into the grooves, for example.In general, the viscosity of the molding composition should besufficiently high that excessive loss of material from the grooves doesnot occur before removal of the volatile liquid.

The grooves may be at least partially (preferably completely) filledwith the molding composition by any suitable technique. In someembodiments, a knife roll coater or vacuum slot die coater can be used.A mold release compound can be used to aid in removing the particlesfrom the mold if desired. Typical mold release agents include, forexample, oils such as peanut oil or mineral oil, fish oil, silicones,polytetrafluoroethylene, zinc stearate, and graphite.

In one embodiment, the top surface of the mold is coated with themolding composition. The molding composition can be pumped onto topsurface. Next, a scraper or leveler bar is used to urge the moldingcomposition fully into the grooves of the mold.

After introducing the molding composition into the grooves, excessmolding composition remaining on the mold surface, if present, can beremoved by a doctor blade or squeegee.

Next, at least some of the volatile liquid is removed; for example, byevaporation using heat, infrared radiation, and/or forced air. Asufficient amount of the volatile liquid should be removed such that themolding composition in the grooves forms dimensionally stable elongateprecursor bodies if removed from the mold. During this process, theexposed longitudinal surface of the molding composition depresses towardits center thereby forming a rounded channel that is concave along itslength. Desirably, the volatile components are removed at a fastevaporation rates. In some embodiments, removal of the volatilecomponent by evaporation occurs at temperatures above the boiling pointof the volatile component. The upper limit to the drying temperatureoften depends on the material the mold is made from. The amount of thevolatile liquid removed will typically vary depending on the compositionof the molding liquid. For example, at least 10 percent, at least 30percent, at least 50 percent, at least 70 percent, at least 90 percent,or even at least 99 percent by weight of the volatile liquid compositionis removed.

Next, at least a portion of the dimensionally stable elongate precursorbodies produced above are converted into the elongate shaped abrasiveparticles, each comprising, respectively, an elongate shaped ceramicbody having opposed first and second ends joined to each other by atleast two longitudinal sidewalls. At least one of longitudinal sidewallsis concave along its length. At least one of the first and second endsis a fractured surface (e.g., one end or both ends). In general, allends except those corresponding to the open ends of the grooves (whichwill be not be molded) will be fractured. Depending on the lengths ofthe grooves and the resultant elongate shaped ceramic bodies, thefraction of elongate shaped abrasive particles produced having twofractured ends may varying. In preferred embodiments, the fraction ofelongate shaped ceramic bodies having two fractured ends may be at least50 percent by weight, 60 percent by weight, 70 percent by weight, 80percent by weight, 90 percent by weight, 95 percent by weight, or even99 percent by weight. If elongate shaped ceramic bodies corresponding tothose formed at the ends of the grooves are removed, then all of theelongate shaped ceramic bodies may have two fractured ends, for example.In some cases it may be possible to fracture at least partially driedmolding material extending beyond the ends of grooves (e.g., if the moldrests on a platen that extends beyond the ends of the grooves), in whichcase, all of the elongate shaped ceramic bodies may also have twofractured ends.

Elongate shaped abrasive particles made according to the presentdisclosure can be incorporated into an abrasive article, or used inloose form. Elongate shaped abrasive particles are generally graded to agiven particle size distribution before use. Such distributionstypically have a range of particle sizes, from coarse particles to fineparticles. In the abrasive art this range is sometimes referred to as a“coarse”, “control”, and “fine” fractions. Elongate shaped abrasiveparticles graded according to abrasive industry accepted gradingstandards specify the particle size distribution for each nominal gradewithin numerical limits. Such industry accepted grading standards (i.e.,abrasive industry specified nominal grade) include those known as theAmerican National Standards Institute, Inc. (ANSI) standards, Federationof European Producers of Abrasive Products (FEPA) standards, andJapanese Industrial Standard (JIS) standards.

Due to the ratio of the length to the width of some elongate shapedabrasive particles, it may be preferred to size the particles based onthe average particle width (“W_(avg)”), the average particle length(“L_(avg)”), and/or the ratio L_(avg)/W_(avg). For example, they mayhave values of: W_(avg)=1110±55 microns and L_(avg)/W_(avg)=1.5 to 3.5;W_(avg)=890±45 microns and L_(avg)/W_(avg)=1.5 to 3.5; W_(avg)=510±26microns and L_(avg)/W_(avg)=2.9 to 4.5; W_(avg)=340±17 microns andL_(avg)/W_(avg)=3.1 to 4.9; W_(avg)=240±12 microns andL_(avg)/W_(avg)=3.3 to 5.1; W_(avg)=240±12 microns andL_(avg)/W_(avg)=3.3 to 5.1; W_(avg)=194±7 microns andL_(avg)/W_(avg)=3.3 to 5.1; W_(avg)=146±6 microns andL_(avg)/W_(avg)=3.3 to 5.1; W_(avg)=132±5 microns andL_(avg)/W_(avg)=3.3 to 5.1.

The width of the elongate shaped abrasive particles may be of anydesired dimension. For example, in some embodiments, the width may be atleast 100 microns, at least 150 microns, at least 200 microns, at least250 microns, at least 500 microns, at least 1000 microns. Likewise, insome embodiments, the width may be, for example, less than 2500 microns,less than 1500 microns, less than 1000 microns, less than 500 microns,less than 400 microns, less than 300 microns, or less than 200 microns.

Elongate shaped abrasive particles according to the present disclosurecan be used in combination with other abrasive particles (e.g., crushedabrasive particles) if desired.

Elongate shaped abrasive particles according to the present disclosuremay be used in a loose form or slurry, and/or incorporated into abrasiveproducts (e.g., bonded abrasives, coated abrasives, and nonwovenabrasives). Criteria used in selecting elongate shaped abrasiveparticles used for a particular abrading application typically include:abrading life, rate of cut, substrate surface finish, grindingefficiency, and product cost.

In one preferred embodiment, the dimensionally stable elongate precursorbodies are separated from the mold, optionally fractured and graded to adesired size distribution, and converted into ceramic elongate shapedceramic bodies by calcining (an optional step), and sintering atelevated temperature. If not previously fractured, the ceramic elongateshaped ceramic bodies can be fractured and graded to a desired sizedistribution.

The dimensionally stable elongate precursor bodies can be removed fromthe grooves by gravity, vibration, ultrasonic vibration, vacuum, orpressurized air, for example. If desired, the dimensionally stableelongate precursor bodies can be further dried outside of the mold.

Optionally, but preferably, the dimensionally stable elongate precursorbodies are calcined at a temperature of from 500° C. to 800° C. forsufficient time (e.g., several hours) to remove bound water and increasedurability in handling. This results in calcined elongate precursorbodies. Sintering may be accomplished in an oven or kiln as described inU.S. Pat. No. 8,142,531 (Adefris et al.), or by passage through a flameas described in PCT International Appln. Publ. No. WO 2014/165390 A1(Erickson et al.).

In another preferred embodiment, the dimensionally stable elongateprecursor bodies are left in the mold (which is made of combustiblematerial), which is heated to burn off the mold and convert them intoceramic elongate shaped ceramic bodies by calcining (an optional step),and sintering at elevated temperature. The ceramic elongate shapedceramic bodies are then fractured and graded to the desired sizedistribution.

Depending on the converting process, the molds may comprise variousmaterials. If combustion is required, then the mold should becombustible, otherwise it may be made of noncombustible material (e.g.,metal, ceramic, glass). Exemplary combustible materials includepolymeric organic materials. Examples of suitable polymeric organicmaterials include thermoplastics such as polyesters, polycarbonates,poly(ether sulfone), poly(methyl methacrylate), polyurethanes,poly(vinyl chloride), polyolefins, polystyrene, polypropylene,polyethylene, combinations of the foregoing, and thermosettingmaterials.

The mold can have a generally planar bottom surface and a plurality ofmold cavities, which may be in a production tool. The production toolcan be a belt, a sheet, a continuous web, a coating roll (e.g., arotogravure roll), a sleeve mounted on a coating roll, or die (e.g., athread rolling die). The production tool may comprise a polymericmaterial. In one embodiment, the tooling is made from a polymeric orthermoplastic material. In another embodiment, the surfaces of thetooling in contact with the sol-gel while drying, such as the surfacesof the plurality of cavities, comprise a polymeric material while otherportions of the tooling can be made from other materials. A suitablecoating may be applied to a metal tooling to change its surface tensionproperties by way of example.

The mold can be made by replication from a master tool, for example,according to known methods. Preferably, the mold is obtained from acommercial source, which may be marketed for a completely unrelatedapplication (e.g., architectural model siding).

A polymeric or thermoplastic tool can be replicated off a metal mastertool. The master tool will have the inverse pattern desired for theproduction tool. The master tool can be made in the same manner as theproduction tool. In one embodiment, the master tool is made out ofmetal, e.g., nickel and is diamond turned. The polymeric sheet materialcan be heated along with the master tool such that the polymericmaterial is embossed with the master tool pattern by pressing the twotogether. A polymeric or thermoplastic material can also be extruded orcast onto the master tool and then pressed. The thermoplastic materialis cooled to solidify and produce the production tool. Further detailconcerning the design and fabrication of production tooling or mastertools can be found in U.S. Pat. No. 5,152,917 (Pieper et al.); U.S. Pat.No. 5,435,816 (Spurgeon et al.); U.S. Pat. No. 5,672,097 (Hoopman etal.); U.S. Pat. No. 5,946,991 (Hoopman et al.); U.S. Pat. No. 5,975,987(Hoopman et al.); and U.S. Pat. No. 6,129,540 (Hoopman et al.).

Molds useful in practice of the present disclosure have open-endedgrooves (including channels), typically extending between edges of themold surface. The grooves may be straight curved, undulating orsquiggly, or a combination thereof. In some preferred embodiments, thegrooves are straight. The grooves may have any transversecross-sectional profile. Examples include, rectangular, triangular,trapezoidal, rounded (e.g., semicircular), and combinations thereof.Importantly, the grooves are independent of one another. For example,the grooves are not fluidly connected to other grooves (e.g., as in alattice groove structure).

Elongate shaped abrasive particles according to the present disclosurecomprise an elongate shaped ceramic body having opposed first and secondends joined to each other by at least two longitudinal sidewalls. Atleast one of the at least two longitudinal sidewalls is concave alongits length. At least one of the first and second ends, preferably both,is a fractured surface.

Referring now to FIG. 2, exemplary elongate shaped abrasive particle 200has an elongate shaped ceramic body 210 having opposed first and secondends 220, 222 joined to each other by longitudinal sidewalls 230, 232.Longitudinal sidewall 230 is concave along its length. First and secondends 220, 222 are fractured surfaces.

Referring now to FIG. 3, exemplary elongate shaped abrasive particle 300has an elongate shaped ceramic body 310 having opposed first and secondends 320, 322 joined to each other by longitudinal sidewalls 330, 332,334, 336. Longitudinal sidewall 330 is concave along its length. Firstand second ends 320, 322 are fractured surfaces.

Elongate shaped abrasive particles according to the present disclosurehave an aspect ratio of at least 2. In some embodiments, the elongateshaped abrasive particles have an aspect ratio of at least 4, at least6, or even at least 10.

The present disclosure further provides a method of abrading a surface.The method comprises contacting an elongate shaped abrasive particleand/or abrasive article (e.g., a bonded abrasive wheel), according tothe present disclosure, with a surface of a workpiece; and moving atleast one of the elongate shaped abrasive particles or the contactedsurface to abrade at least a portion of the surface with the elongateshaped abrasive particle and/or abrasive article. Methods for abradingwith elongate shaped abrasive particles made according to the presentdisclosure range from snagging (i.e., high pressure high stock removal)to polishing (e.g., polishing medical implants with coated abrasivebelts), wherein the latter is typically done with finer grades ofelongate shaped abrasive particles. The elongate shaped abrasiveparticles may also be used in precision abrading applications, such asgrinding cam shafts with vitrified bonded wheels. The size of theelongate shaped abrasive particles used for a particular abradingapplication will be apparent to those skilled in the art.

Abrading with elongate shaped abrasive particles according to thepresent disclosure may be done dry or wet. For wet abrading, the liquidmay be introduced in the form of a light mist to complete flood.Examples of commonly used liquids include: water, water-soluble oil,organic lubricant, and emulsions. The liquid may serve to reduce theheat associated with abrading and/or act as a lubricant. The liquid maycontain minor amounts of additives such as bactericide, antifoamingagents, and the like.

Elongate shaped abrasive particles made according to the presentdisclosure may be useful, for example, to abrade workpieces such asaluminum metal, carbon steels, mild steels, tool steels, stainlesssteel, hardened steel, titanium, glass, ceramics, wood, wood-likematerials (e.g., plywood and particle board), paint, painted surfaces,organic coated surfaces and the like. The applied force during abradingtypically ranges from about 1 to about 100 kilograms.

Bonded abrasive articles typically include a shaped mass of abrasiveparticles (e.g., elongate shaped abrasive particles according to thepresent disclosure) held together by an organic, metallic, or vitrifiedbinder. Such shaped mass can be, for example, in the form of a wheel,such as a grinding wheel or cutoff wheel. The diameter of grindingwheels typically is about 1 cm to over 1 meter; the diameter of cut offwheels about 1 cm to over 80 cm (more typically 3 cm to about 50 cm).The cut off wheel thickness is typically about 0.5 mm to about 5 cm,more typically about 0.5 mm to about 2 cm. The shaped mass can also bein the form, for example, of a honing stone, segment, mounted point,disc (e.g., double disc grinder) or other conventional bonded abrasiveshape. Bonded abrasive articles typically comprise about 3-50 percent byvolume of bond material, about 30-90 percent by volume of the elongateshaped abrasive particles (or a blend thereof of with crushed abrasiveparticles), up to 50 percent by volume additives (including grindingaids), and up to 70 percent by volume pores, based on the total volumeof the bonded abrasive article.

An exemplary grinding wheel is shown in FIG. 4. Referring now to FIG. 4,grinding wheel 400 is depicted, which includes elongate shaped abrasiveparticles made according to the present disclosure 410 in a bindermaterial 420 (e.g., an organic binder or a vitreous binder), molded intoa wheel and mounted on hub 430.

Suitable organic binders for making bonded abrasive articles includethermosetting organic polymers. Examples of suitable thermosettingorganic polymers include phenolic resins, urea-formaldehyde resins,melamine-formaldehyde resins, urethane resins, acrylate resins,polyester resins, aminoplast resins having pendant α,β-unsaturatedcarbonyl groups, epoxy resins, acrylated urethane, acrylated epoxies,and combinations thereof. The binder and/or abrasive article may alsoinclude additives such as fibers, lubricants, wetting agents,thixotropic materials, surfactants, pigments, dyes, antistatic agents(e.g., carbon black, vanadium oxide, and/or graphite), coupling agents(e.g., silanes, titanates, and/or zircoaluminates), plasticizers,suspending agents, and the like. The amounts of these optional additivesare selected to provide the desired properties. The coupling agents canimprove adhesion to the elongate shaped abrasive particles and/orfiller. The binder chemistry may be thermally cured, radiation cured orcombinations thereof. Additional details on binder chemistry may befound in U.S. Pat. No. 4,588,419 (Caul et al.); U.S. Pat. No. 4,751,138(Turney et al.), and U.S. Pat. No. 5,436,063 (Follett et al.).

Vitreous binders, which exhibit an amorphous structure and are typicallyhard, are well known in the art. In some cases, the vitreous bindersinclude crystalline phases. Bonded, vitrified abrasive articles madeaccording to the present disclosure may be in the shape of a wheel(including cut off wheels), honing stone, mounted pointed or otherconventional bonded abrasive shape. In some embodiments, a vitrifiedbonded abrasive article made according to the present disclosure is inthe form of a grinding wheel.

Vitreous binders can be made by heating various of metal oxides such as,for example, silica, silicates, alumina, soda, calcia, potassia,titania, iron oxide, zinc oxide, lithium oxide, magnesia, boria,aluminum silicate, borosilicate glass, lithium aluminum silicate, andcombinations thereof. Typically, vitreous binders can be formed fromcompositions comprising from 10 to 100 percent of glass frit, althoughmore typically the composition comprises 20 to 80 percent of glass frit,or 30 to 70 percent of glass frit. The remaining portion of the vitreousbonding material can be a non-frit material. Alternatively, the vitreousbond may be derived from a non-fit containing composition. Vitreousbonding materials are typically matured at a temperature(s) in a rangeof about 700° C. to about 1500° C., usually in a range of about 800° C.to about 1300° C., sometimes in a range of about 900° C. to about 1200°C., or even in a range of about 950° C. to about 1100° C. The actualtemperature at which the binder (also known as “bond”) is matureddepends, for example, on the particular bond chemistry.

In some embodiments, vitrified binders include those comprising silica,alumina (desirably, at least 10 percent by weight alumina), and boria(desirably, at least 10 percent by weight boria). In most cases, thevitrified bonding material further comprises alkali metal oxide(s)(e.g., Na₂O and K₂O) (in some cases at least 10 percent by weight alkalimetal oxide(s)).

Binder materials may also contain filler materials or grinding aids,typically in the form of a particulate material. Typically, theparticulate materials are inorganic materials. Examples of usefulfillers for the present disclosure include: metal carbonates (e.g.,calcium carbonate (e.g., chalk, calcite, marl, travertine, marble andlimestone), calcium magnesium carbonate, sodium carbonate, magnesiumcarbonate), silica (e.g., quartz, glass beads, glass bubbles and glassfibers) silicates (e.g.; talc, clays, (montmorillonite) feldspar, mica,calcium silicate, calcium metasilicate, sodium aluminosilicate, sodiumsilicate) metal sulfates (e.g., calcium sulfate, barium sulfate, sodiumsulfate, aluminum sodium sulfate, aluminum sulfate), gypsum,vermiculite, wood flour, aluminum trihydrate, carbon black, metal oxides(e.g., calcium oxide (lime), aluminum oxide, titanium dioxide), andmetal sulfites (e.g., calcium sulfite).

In general, the addition of a grinding aid increases the useful life ofthe abrasive article. A grinding aid is a material that has asignificant effect on the chemical and physical processes of abrading,which results in improved performance. Although not wanting to be boundby theory, it is believed that a grinding aid(s) will (a) decrease thefriction between the abrasive particles and the workpiece being abraded,(b) prevent the abrasive particles from “capping” (i.e., prevent metalparticles from becoming welded to the tops of the abrasive particles),or at least reduce the tendency of abrasive particles to cap, (c)decrease the interface temperature between the abrasive particles andthe workpiece, or (d) decreases the grinding forces.

Grinding aids encompass a wide variety of different materials and can beinorganic or organic based. Examples of chemical groups of grinding aidsinclude waxes, organic halide compounds, halide salts and metals andtheir alloys. The organic halide compounds will typically break downduring abrading and release a halogen acid or a gaseous halide compound.Examples of such materials include chlorinated waxes liketetrachloronaphthalene, pentachloronaphthalene, and polyvinyl chloride.Examples of halide salts include sodium chloride, potassium cryolite,sodium cryolite, ammonium cryolite, potassium tetrafluoroborate, sodiumtetrafluoroborate, silicon fluorides, potassium chloride, and magnesiumchloride. Examples of metals include, tin, lead, bismuth, cobalt,antimony, cadmium, and iron titanium. Other miscellaneous grinding aidsinclude sulfur, organic sulfur compounds, graphite, and metallicsulfides. It is also within the scope of the present disclosure to use acombination of different grinding aids, and in some instances this mayproduce a synergistic effect.

Bonded abrasive articles can contain 100 percent elongate shapedabrasive particles according to the present disclosure, or blends ofsuch abrasive particles with other abrasive particles and/or diluentparticles. However, at least about 2 percent by weight, desirably atleast about 5 percent by weight, and more desirably about 30 to 100percent by weight, of the abrasive particles in the abrasive articlesshould be elongate shaped abrasive particles made according to thepresent disclosure. In some instances, the elongate shaped abrasiveparticles made according to the present disclosure may be blended withother abrasive particles and/or diluent particles at a ratio between 5to 75 percent by weight, about 25 to 75 percent by weight, about 40 to60 percent by weight, or about 50 to 50 percent by weight (i.e., inequal amounts by weight). Examples of suitable conventional abrasiveparticles include fused aluminum oxide (including white fused alumina,heat-treated aluminum oxide and brown aluminum oxide), silicon carbide,boron carbide, titanium carbide, diamond, cubic boron nitride, garnet,fused alumina-zirconia, and sol-gel-derived abrasive particles, abrasiveagglomerates, and combinations thereof.

In some instances, a blend of abrasive particles may result in a bondedabrasive article that exhibits improved grinding performance incomparison with bonded abrasive articles comprising 100 percent ofeither type of abrasive particle. If there is a blend of abrasiveparticles, the abrasive particle types forming the blend may be of thesame size. Alternatively, the abrasive particle types may be ofdifferent particle sizes.

Examples of suitable diluent particles include marble, gypsum, flint,silica, iron oxide, aluminum silicate, glass (including glass bubblesand glass beads), alumina bubbles, alumina beads and diluentagglomerates.

The abrasive particles may be uniformly distributed in the abrasivearticle or concentrated in selected areas or portions of the abrasivearticle. For example, in a bonded abrasive, there may be two distinctsections of the grinding wheel. The outermost section may compriseabrasive particles made according to the present disclosure, whereas theinnermost section does not. Alternatively, elongate shaped abrasiveparticles made according to the present disclosure may be uniformlydistributed throughout the bonded abrasive article. Further detailsregarding resin bonded abrasive articles can be found, for example, inU.S. Pat. No. 4,543,107 (Rue); U.S. Pat. No. 4,741,743 (Narayanan etal.); U.S. Pat. No. 4,800,685 (Haynes et al.); U.S. Pat. No. 4,898,597(Hay et al.); U.S. Pat. No. 4,997,461 (Markhoff-Matheny et al.); U.S.Pat. No. 5,037,453 (Narayanan et al.); U.S. Pat. No. 5,110,332(Narayanan et al.); and U.S. Pat. No. 5,863,308 (Qi et al.). Furtherdetails regarding vitreous bonded abrasives can be found, for example,in U.S. Pat. No. 4,543,107 (Rue); U.S. Pat. No. 4,898,597 (Hay et al.);U.S. Pat. No. 4,997,461 (Markhoff-Matheny et al.); U.S. Pat. No.5,094,672 (Giles Jr. et al.); U.S. Pat. No. 5,118,326 (Sheldon et al.);U.S. Pat. No. 5,131,926 (Sheldon et al.); U.S. Pat. No. 5,203,886(Sheldon et al.); U.S. Pat. No. 5,282,875 (Wood et al.); U.S. Pat. No.5,738,696 (Wu et al.), and U.S. Pat. No. 5,863,308 (Qi).

Select Embodiments of the Present Disclosure

In a first embodiment, the present disclosure provides an elongateshaped abrasive particle comprising an elongate shaped ceramic bodyhaving opposed first and second ends joined to each other by at leasttwo longitudinal sidewalls, wherein at least one of the at least twolongitudinal sidewalls is concave along its length, and wherein at leastone of the first and second ends is a fractured surface.

In a second embodiment, the present disclosure provides an elongateshaped abrasive particle according to the first embodiment, wherein saidat least two longitudinal sidewalls consist of two longitudinalsidewalls, and wherein the elongate shaped ceramic body has a continuouscrescent-shaped cross-sectional shape.

In a third embodiment, the present disclosure provides an elongateshaped abrasive particle according to the first embodiment, wherein saidat least two longitudinal sidewalls comprise four longitudinalsidewalls, two of which are parallel.

In a fourth embodiment, the present disclosure provides an elongateshaped abrasive particle according to any of the first to thirdembodiments, wherein the elongate shaped ceramic body has an aspectratio of at least two.

In a fifth embodiment, the present disclosure provides an elongateshaped abrasive particle according to any of the first to fourthembodiments, wherein the elongate shaped ceramic body has an aspectratio of at least ten.

In a sixth embodiment, the present disclosure provides an elongateshaped abrasive particle according to any of the first to fifthembodiments, wherein the elongate shaped ceramic body comprises alphaalumina.

In a seventh embodiment, the present disclosure provides a plurality ofabrasive particles, wherein at least half of the plurality of abrasiveparticles comprise elongate shaped abrasive particles according to anyof the first to sixth embodiments.

In an eighth embodiment, the present disclosure provides a bondedabrasive article comprising a plurality of abrasive particles accordingto the seventh embodiment bonded together by a binder material.

In a ninth embodiment, wherein the binder material comprises a vitreousbinder material.

In a tenth embodiment, the present disclosure provides a bonded abrasivearticle according to the eighth embodiment, wherein the binder materialcomprises an organic binder material.

In an eleventh embodiment, the present disclosure provides a bondedabrasive article according to any of the eighth to tenth embodiments,wherein the bonded abrasive article comprises a bonded abrasive wheel.

In a twelfth embodiment, the present disclosure provides a method ofmaking a plurality of elongate shaped abrasive particles, the methodcomprising sequential steps:

-   -   a) providing a mold having a plurality of isolated open-ended        grooves disposed on a major surface thereof;    -   b) filling at least a portion of the plurality of isolated        open-ended grooves with a molding composition comprising a        ceramic precursor material and a volatile liquid;    -   c) removing any excess molding composition not disposed within        the plurality of isolated open-ended grooves, if present, from        the mold;    -   d) removing a sufficient amount of the liquid vehicle to provide        a plurality of dimensionally stable elongate precursor bodies;        and    -   e) converting at least a portion of the plurality of        dimensionally stable elongate precursor bodies into the elongate        shaped abrasive particles, each comprising, respectively, an        elongate shaped ceramic body having opposed first and second        ends joined to each other by at least two longitudinal        sidewalls, wherein at least one of the at least two longitudinal        sidewalls is concave along its length, and wherein at least one        of the first and second ends is a fractured surface.

In a thirteenth embodiment, the present disclosure provides a methodaccording to the twelfth embodiment, wherein step e) comprisesseparating the plurality of dimensionally stable elongate precursorbodies from the mold, fracturing the plurality of dimensionally stableelongate precursor bodies, and heating the fractured plurality ofdimensionally stable elongate precursor bodies to convert them into theelongate shaped abrasive particles.

In a fourteenth embodiment, the present disclosure provides a methodaccording to the twelfth embodiment, wherein step e) comprisesseparating the plurality of dimensionally stable elongate precursorbodies from the mold, heating the plurality of dimensionally stableelongate precursor bodies to convert them into elongate ceramic bodies,and fracturing the elongate ceramic bodies to convert them into theelongate shaped abrasive particles.

In a fifteenth embodiment, the present disclosure provides a methodaccording to any one of the twelfth to fourteenth embodiments, whereinthe molding composition comprises a sol-gel material.

In a sixteenth embodiment, the present disclosure provides a methodaccording to the fifteenth embodiment, wherein the molding compositioncomprises a sol-gel alpha alumina precursor.

In a seventeenth embodiment, the present disclosure provides a methodaccording to any one of the twelfth to sixteenth embodiments, whereinthe molding composition comprises alpha alumina particles.

Objects and advantages of this disclosure are further illustrated by thefollowing non-limiting examples, but the particular materials andamounts thereof recited in these examples, as well as other conditionsand details, should not be construed to unduly limit this disclosure.

EXAMPLES

Unless otherwise noted, all parts, percentages, ratios, etc. in theExamples and the rest of the specification are by weight.

Unless stated otherwise, all other reagents were obtained, or areavailable from fine chemical vendors such as Sigma-Aldrich Company, St.Louis, Mo., or may be synthesized by known methods.

Example 1

A sample of boehmite sol-gel was made using the following recipe: 1600parts of DISPERAL aluminum oxide monohydrate powder (Sasol North AmericaInc., Houston, Tex.) was dispersed by high shear mixing a solutioncontaining 2400 parts of deionized water and 72 parts of 70% aqueousnitric acid. The resulting sol-gel was aged for 1 hour. The resultingsol-gel was forced into a grooved styrene sheet (obtained as #4530 0.125INCH OPAQUE WHITE STYRENE SHEET from Evergreen Scale Models Company, DesPlaines, Ill.) having a topical coating of peanut oil obtained bybrushing about 2 grams of a 1 percent by weight peanut oil solution inmethanol onto the 12 inches (30.5 cm)×6 inches (15.2 cm) sheet. Thesol-gel was spread to the sheet using a putty knife so that the grooveswere completely filled. The sheet containing the sol-gel was then airdried for two hours. Following drying, the sheet was shaken to dislodgethe resulting precursor shaped particles. The precursor particles nowconsisted of various lengths with shaped cross section according to thegrooves on sheet.

The precursor shaped abrasive particles were calcined by heating them toapproximately 650 degrees Celsius (° C.) in air for 15 minutes, thensaturated with a mixed nitrate solution of the following concentrations(reported as oxides): 1.8 percent each of MgO, Y₂O₃, Nd₂O₃ and La₂O₃.The excess nitrate solution was removed, and the saturated precursorshaped abrasive particles were allowed to dry after which the particleswere again calcined at 650° C., and then sintered at approximately 1400°C. Both the calcining and sintering was performed using rotary tubekilns Elongate shaped abrasive particles produced by the above methodare shown in FIG. 5.

Performance Test of Example 1 and Comparative A

Elongate shaped abrasive particles made in Example 1 were manuallybroken using a razor blade to produce particles of lengths of no morethan approximately 3 millimeters. The abrasive particles were sievedthrough a set of USA Standard Testing Sieves with sizes 25, 30, 35, and40. Approximately 85% of the abrasive particles were retained on the 30and 35 mesh screens. The fraction retained on the 30 mesh screen wascollected and used to make a coated abrasive disc. The coated abrasivedisc was made according to conventional procedures. Twelve grams of theshaped abrasive particles were bonded to 17.8 cm diameter, 0.8 mm thickvulcanized fiber backings (having a 2.2 cm diameter center hole) using aconventional calcium carbonate-filled phenolic make resin (48 weightpercent of resole phenolic resin, 52 weight percent of calciumcarbonate, diluted to 81 weight percent solids with water and glycolether) and a conventional cryolite-filled phenolic size resin (32 weightpercent of resole phenolic resin, 2 weight percent of iron oxide, 66weight percent of cryolite, diluted to 78 weight percent of solids withwater and glycol ether). The wet make resin weight was about 185 gramsper square meter Immediately after the make coat was applied, the shapedabrasive particles were electrostatically coated. The make resin washeated for 120 minutes at 88° C. Then, the cryolite-filled phenolic sizecoat was coated over the make coat and abrasive particles. The wet sizeweight was about 850 grams per square meter. The size resin was heatedfor 12 hours at 99° C. The coated abrasive disc was flexed prior totesting.

Comparative Example A coated abrasive discs were prepared as describedabove, except that conventional crushed sol-gel-derived alumina abrasiveparticles (3M CERAMIC ABRASIVE GRAIN 321, 3M Company, St. Paul, Minn.)were used in place of the elongate shaped abrasive particles made inExample 1.

The performance of coated abrasive discs using the Example 1 andComparative Example A abrasive particles was evaluated as follows. Eachcoated abrasive disc for evaluation was attached to a rotary grinderfitted with a 7-inch (17.8 centimeters) ribbed disc pad face plate(80514 EXTRA HARD RED, 3M Company). The grinder was then activated andurged against an end face of a 0.75 inch (1.9 cm)×0.75 inch (1.9 cm)pre-weighed 1045 steel bar under a load of 10 pounds (4.5 kg). Theresulting rotational speed of the grinder under this load and againstthis workpiece was 5000 revolutions per minute. The workpiece wasabraded under these conditions for a total of fifty 20-second grindingintervals (passes). Following each 20-second interval, the workpiece wasallowed to cool to room temperature and weighed to determine the cut ofthe abrasive operation. Test results were reported as the incrementalcut for each interval and the total cut removed. The total cut was thesum of the amount of material removed from the workpiece throughout thetest period. The test results are reported in Table I, below.

TABLE I 1045 STEEL CUMULATIVE CUT, grams COMPARATIVE GRINDING PASSESEXAMPLE 1 EXAMPLE A 10 195 201 20 346 362 30 510 490 40 671 581 50 808660

Example 2

A sample of alumina slurry was prepared using the following recipe: 7851part of alumina powder (RG 4000, Almatis, Theemsweg, Netherlands) wasdispersed by mixing 1963 parts of deionized water and 17 parts ofanhydrous citric acid. The resulting mixture was milled at 1700revolutions per minute for 0.5 hours to produce a smooth and creamyslurry. After completion of the milling, 169 parts of a binder solutionconsisting of 6.67 weight percent of magnesium citrate, 16.97 weightpercent of cellulose gum (BLANOSE from Hercules, Inc., Wilmington,Del.), and 76.36 weight percent of deionized water was were thoroughlystirred into the mixture. The resulting alumina slurry was forced into agrooved polypropylene microreplicated tooling. A scanning electronmicroscope (SEM) micrograph (JEOL MODEL 7600F scanning electronmicroscope, JEOL, Tokyo, Japan) of the surface of the tooling is shownin FIG. 6A and an SEM micrograph of the side view of the tooling isshown in FIG. 6B. The microreplicated tooling contained a series ofgrooves with curved sidewalls that intersected to form a line at thebase of the groove. The width of the grooves varied from approximately0.5 millimeters to over 1 millimeter, and the depths were all 0.5millimeters.

Before the slurry was applied to the microreplicated tooling, thetooling was topically coated with peanut oil (approximately 1.55 gramper square meter) onto the surface of the polypropylene tooling. Theslurry was spread to the tooling using a squeegee so that the grooveswere completely filled. The tooling containing the slurry was thenallowed to dry in a forced air oven at approximately 82.2° C. Followingdrying, the tooling was allowed to dislodge the resulting precursorshaped particles, which were shaped according to the grooves incross-section. The precursor particles were crushed to produce particlesof lengths of no more than approximately 6.4 millimeters. The precursorabrasive particles were fired to 1515° C. for 3 hours to form elongateshaped abrasive particles. SEM micrographs of the resulting elongateshaped abrasive particles are shown in FIGS. 7A and 7B.

The densities of the resultant sintered shaped abrasive particles weremeasured with the use of an ACCUPYC II 1330 pycnometer fromMicromeritics Instrument Corporation, Norcross, Ga., according tostandard operating procedure. The true density of the sintered shapedabrasive particles prepared from the above method was measured atapproximately 3.85 grams per cubic centimeter.

Performance Test of Example 2 and Comparatives B, C

The abrasive particles made form Example 2 were graded through USAStandard Testing Sieves and the abrasive particles obtained from −30+35mesh sieves were used to make depressed center grinding wheels. A Type27 depressed-center composite grinding wheel was prepared as follows. Amix was prepared by combining 860 grams abrasive particles obtained fromthe above procedure, 55 grams liquid phenolic resin (obtained undertrade designation “PREFERE 825136G1” from Dynea Oy Corporation,Helsinki, Finland), 155 grams phenolic resin powder (obtained undertrade designation “VARCUM 29302” from Durez Corporation, Niagara Falls,N.Y.) and 155 grams sodium hexafluoroaluminate (obtained under tradedesignation “CRYOLITE” from Freebee, Ullerslev, Denmark) and mixed for10 minutes using a paddle-type mixer (CUISINART SM-70 from ConairCorporation, East Windsor, N.J., operated at speed 1). A 4.5-inch (11.4centimeters) diameter disc of fiberglass mesh scrim (obtained under thetrade designation “PS 660” from Swatycomet, Maribor, Slovenia) wasplaced into a 4.5-inch (11.4 centimeters) diameter cavity die. The mix(75 grams) was spread out evenly. A second 4-inch (10.2 centimeters)diameter of fiberglass mesh scrim (PS 660, from Swatycomet) was placedon top of the mixture. Then additional mix (75 grams) was spread outevenly. A third 3-inch (7.4 centimeters) diameter of fiberglass meshscrim (PS 660 from Swatycomet) was placed on top. The filled cavity moldwas then pressed at a pressure of 40 tons/38 square inches (14.5 MPa).The resulting wheel was removed from the cavity mold and placed on aspindle between depressed center aluminum plates in order to be pressedinto a Type 27 depressed-center grinding wheel. The wheel was compressedat 5 ton/38 square inches (1.8 MPa) to shape the disc. The wheel wasthen placed in an oven to cure for 7 hours at 79° C., 3 hours at 107°C., 18 hours at 185° C., and a temperature ramp-down over 4 hours to 27°C. The dimensions of the final grinding wheel were 180 mm diameter×7 mmthickness. The center hole was ⅞ inch (2.2 cm) in diameter.

Comparative Examples B was a 4½ inch (11.4 cm) BLUEFIRE DEPRESSED CENTERWHEEL (Type 27) from Saint-Gobain S.A., Courbevoie, France.

Comparative Example C was obtained as a GREEN CORPS CUTTING/GRINDINGWHEEL—4½ INCH (11.4 cm) (Type 27) from 3M Company.

Abrasive wheels were tested by grinding a rectangular mild steel bar(0.25 inch (0.6 cm)×18 inches (45.7 cm)×3 inches (7.6 cm)) over a 0.25inch (0.6 cm)×18 inches (45.7 cm) area of the surface while mounted onan air driven grinder (operated at 12000 revolutions per minute) thatoscillated back and forth for ten one-minute cycles. Each cycle is for atotal of 36 inches (91.4 cm) with 18 inches (45.7 cm) each way. Theapplied load was the grinder weight of 9 pounds (4.1 kilograms) and theabrasive wheel was held at an angle of 15 degrees relative to thesurface. The steel bar was weighed before and after each cycle, and thetotal cut (the total weight loss of the steel bar) was recorded afterthe 10-cycle test. Test results are reported in TABLE 2, below.

TABLE 2 Total Cut, grams Example 2 254 Comparative 219 Example BComparative 144 Example C

Various modifications and alterations of this disclosure may be made bythose skilled in the art without departing from the scope and spirit ofthis disclosure, and it should be understood that this disclosure is notto be unduly limited to the illustrative embodiments set forth herein.

All cited references, patents, and patent applications in the aboveapplication for letters patent are herein incorporated by reference intheir entirety in a consistent manner. In the event of inconsistenciesor contradictions between portions of the incorporated references andthis application, the information in the preceding description shallcontrol. The preceding description, given in order to enable one ofordinary skill in the art to practice the claimed disclosure, is not tobe construed as limiting the scope of the disclosure, which is definedby the claims and all equivalents thereto.

What is claimed is:
 1. A bonded abrasive article comprising a pluralityof abrasive particles bonded together by a binder material, wherein atleast half of the plurality of abrasive particles comprises elongateshaped abrasive particles each comprising an elongate shaped ceramicbody having opposed first and second ends joined to each other by atleast two longitudinal sidewalls, wherein at least one of the at leasttwo longitudinal sidewalls is concave along its length, and wherein atleast one of the first and second ends is a fractured surface.
 2. Thebonded abrasive article of claim 1, wherein the binder materialcomprises a vitreous binder material.
 3. The bonded abrasive article ofclaim 1, wherein the binder material comprises an organic bindermaterial.
 4. The bonded abrasive article of claim 1, wherein said atleast two longitudinal sidewalls consist of two longitudinal sidewalls,and wherein the elongate shaped ceramic body has a continuouscrescent-shaped cross-sectional shape.
 5. The bonded abrasive article ofclaim 1, wherein said at least two longitudinal sidewalls comprise fourlongitudinal sidewalls, two of which are parallel.
 6. The bondedabrasive article of claim 1, wherein the elongate shaped ceramic bodyhas an aspect ratio of at least two.
 7. The bonded abrasive article ofclaim 1, wherein the elongate shaped ceramic body has an aspect ratio ofat least ten.
 8. The bonded abrasive article of claim 1, wherein theelongate shaped ceramic body comprises alpha alumina.